The major shrimp allergen is now known to be shrimp tropomyocin. Antigenic as well as allergenic activities are associated with at least two peptides that are similar between Crustaceae, but vary between tropomyosins from phylogenetically distant species. Synthetic peptides corresponding to IgE binding B-cell epitopes have comparable allergenicity to native peptides. T-cell epitopes are now being identified. Pollen of Parthenium hysterophorus is a major cause of allergic rhinitis throughout the world. We have now purified a 31 kDa acidic glycoprotein, rich in glycine and proline, from Parthenium hysterophorus (designated as Par h 1). Pronase digestion, periodate oxidation and chemical deglycosylation experiments strongly suggest that the oligosaccharides covalently linked to the polypeptide backbone of Par h 1 contribute significantly towards its binding to IgE antibodies. The N-terminal sequence shows a strong identity with an anther-specific cell wall protein. The hydroxyproline-rich region of Par h 1 also exhibits partial identity in a 30-40 amino acid sequence to extensins, a class of hydroxyproline-rich cell wall glycoproteins from maize, tobacco, Sorghum and carrot. Antibodies to Par h 1 cross-react with an extensin precursor from potato tuber. This data is consistent with the conclusion that, like crustacean tropomyosins and plant profilins, a group of soluble plant glycoproteins related to the ubiquitous extensins have certain common IgE binding epitopes that contribute to allergenic cross- reactivity among specific pollens and foods.